Gas streams often carry particulate material. In many instances, it is desirable to remove some or all of the particulate material from a gas flow stream. For example, air intake streams to engines for motorized vehicles or power generation equipment, gas streams directed to gas turbines, and air streams to various combustion furnaces, often include entrained particulate material. The particulate material, should it reach the internal workings of the various mechanisms involved, can cause substantial damage. Removal of the particulate material from the gas flow upstream of the engine, turbine, furnace, or other equipment involved is often needed. Another example is the commercial and residential heating, ventilating, and air conditioning (HVAC) filter system. Air streams to HVAC system often carry particulate material such as pollens, spores, atmospheric dust, and other sub-micron particles. Removal of the particulate material is desirable to reduce allergic reaction as well as potential health risks.
In filtration applications, it is commonly known to pleat the filter medium in order to increase the effective surface area available for fluid impact. The melt-blown synthetic media producers combine an electrostatically charged microfiber web with a scrim support layer to achieve acceptable initial filtration efficiency and filter resistance. If the microfiber web is melt blown, then the melt-blown layer typically consists of 15-40 gsm fiber of 1-5 microns in diameter and thickness of layer is about 0.2-0.4 mm. There are deficiencies to this kind of product. The total thickness of media is typically greater than 0.6 mm, which once pleated the thickness contributes to flow resistance. As the melt-blown layer is relatively thick, the flow pattern through the layer is not completely perpendicular to the layer and the tangential flow could result in higher resistance. Media that are initially charged typically lose electrostatic charge due to heat, humidity, and dust accumulation, which results in decrease in filtration efficiency.
The present invention overcomes the limitations associated with the flow resistance in pleated melt blown structures, and the decrease in efficiency with use associated with charged media.